A modern day data communication system is typically a network of processors and peripherals interconnected to move data between sources and users spread over a large geographical area. The architecture of a typical data network may involve many design tradeoffs that are specific to the intended application of the network, but the complete description of the network will include specifications of the network topology, communication protocols, hardware and transmission media and links.
The topology of a network is a pattern or diagram of its interconnectivity. The earliest computer time-sharing networks were connected in a simple star configuration, which is appropriate when the terminals communicate only with the central computer. More complex configurations, such as meshes of trees, may be appropriate for applications in which terminals and processors communicate with each other. The ring topology is a common configuration used in many local-area networks.
Available transmission media include air (e.g., in terrestrial line-of-sight microwave or satellite systems), coaxial cable, paired copper cable and fiber optic cable. Many different systems having different band widths, modulation techniques, frequency bands, etc., have been developed for each type of transmission medium. The best combination of characteristics for a particular system would depend upon the intended application and environment of that system. In many environments, e.g., in an electrical substation, reliability and cost are the paramount concerns; i.e., the network should be highly reliable and yet be reasonably inexpensive.